This invention is directed to the interaction between integrin β3 and talin, including a chimeric peptide that has high affinity for talin, muteins of integrin β3 and talin, and screening methods for identifying agents that can disrupt the interaction, which provides a new therapeutic target.
Regulation of integrin affinity (activation) is essential for metazoan development and for many pathological processes. Integrins are found throughout the animal kingdom where they play important roles in cell adhesion, migration, proliferation, and survival. They are membrane-spanning heterodimers of α and β subunits, both of which typically comprise a short cytoplasmic tail (˜20 to 50 residues), a single transmembrane helix, and a large extracellular domain (˜700 to 1000 residues). In mammals, there are eighteen identified α subunits and eight β subunits that combine to form 24 distinct heterodimers. In humans, integrins play critical roles in development and participate in the pathogenesis of heart disease, chronic inflammation, and cancer.
Many integrins are expressed with their extracellular domains in a default low-affinity ligand binding state (the “off state”); however, cells can change the conformation and affinity of these receptors in response to cellular stimulation, a process often termed “integrin activation.” This conformation change results in increased adhesion and subsequent signaling, mediating events such as cell migration, platelet aggregation, leukocyte exit from the vasculature, and assembly of the extracellular matrix. The binding of a cytoskeletal protein, called talin, to the β subunit cytoplasmic tail is a common final step in the activation process.
Because integrin activation is involved in pathophysiological processes leading to such conditions as cancer, heart disease including myocardial infarction, and rheumatoid arthritis, there have been a number of pharmacological efforts to control such activation. One route that has been tried is integrin antagonists such as ReoPro (abciximab), Integrilin (eptifibatide), Aggrestat (tirofiban), Raptiva, or Tysabri (natalizumab). These bind to and block all integrin function. The blockage of all integrin function can lead to substantial side effects. For example, the administration of Tysabri (natalizumab) for treatment of multiple sclerosis was shown in rare cases to lead to the development of progressive multifocal leukoencephalopathy, causing suspension of approval of Tysabri. Another route that has been tried is the use of anti-thrombotics that block integrin activation indirectly. Although some of these drugs, such as Plavix (clopidogrel), naproxen, or acetylsalicylic acid (aspirin), are useful, they also have very wide ranging effects and have significant side effects that limit their use in many patients.
Therefore, there is a need to develop targets of pharmacological action that are specific to the integrin and have specific mechanism-based effects. This will result in fewer side effects and enable their use in a wider variety of patients.